1. Field of the Invention
The invention relates to a process for producing a lightweight molded part in which a metal foam is formed out of a particle-containing, molten metal by introducing gas or gas mixtures into the melt, the melt is introduced at least partially into a casting die, and the liquid phase is allowed to solidify therein.
The invention further comprises a lightweight molded part made of metal foam, comprising a metal matrix in which particles are embedded and which encloses a plurality of essentially spherical and/or essentially ellipsoid voids.
2. Discussion of Background Information
Molded parts made of metal foam naturally have a low density and, due to their structure, have special mechanical material properties. For instance, such parts can be given large deformations with upsetting degrees up to 70% and more with the application of two-or three-dimensional compressive strains. These materials with special properties can be advantageously used in technical applications, e.g., as energy absorbers in automotive technology and the like.
When using such molded parts for selected functions with certain parameters, it is important to ensure identical and reproducible property characteristics of the materials.
A process for producing a particle-reinforced metal foam is known from EP 483 184 B, the entire disclosure of which is expressly incorporated herein by reference. According to this document cellulating gas is introduced into a metal melt having reinforcing agents finely distributed therein, metal foam composite material is formed, and the accumulated foam is removed from the surface of the melted material and allowed to solidify. However, this metal foam has bubbles with uncontrolled size or size distribution, which results in a highly diffused property profile of the foam or molded part and causes functional uncertainties.
According to EP 545 957 B1 and U.S. Pat. No. 5,221,324, expressly incorporated herein by reference in their entireties, another lightweight metal part has a plurality of closed and isolated, generally spherical pores with sizes in range of 10 to 500 μm. Although such small pores with large differences in diameter can provide a metal part made with aluminum with a lower specific gravity in comparison with the bulk material, it usually is impossible to achieve a density of less than 1.0 g/cm3 and an upsetting degree of more than 60% under defined conditions.
A number of sequentially operating (U.S. Pat. No. 5,281,251, DE 43 26 982 C1) and/or continuously operating (U.S. Pat. No. 5,334,236, EP 544 291 A1, DE 43 26 982 C1, WO 91/03578) processes and devices have been proposed for producing various shapes of lightweight parts made of metal foam, with which processes and devices articles which are quite operable on principle can be produced. However, the mechanical properties thereof cannot be adjusted with the precision which is often required. The entire disclosures of the above documents are expressly incorporated herein by reference.